Bud'ko, S. L., O. Nakamura, J. Guimpel, M. Maple, and I. K. Schuller. "Anisotropic pressure dependence of the critical temperature of REBa2Cu3O7−δ." Physica C: Superconductivity 185-189, Part 3 (1991): 1947–1948.
Abstract: The hydrostatic pressure dependence of the superconducting critical temperature, Tc, was measured in highly crystalline oriented REBa2Cu3O7−δ (RE=Yb, Dy, Y, Gd) thin films grown on different substrates. The anisotropic strain field induced by the substrate and the different crystalline orientations of the films allows the three strain derivatives of the critical temperature to be estimated. A large anisotropy is found in the ab plane with Tc increasing on compression parallel to the CuO chains and decreasing on compression perpendicular to them. The results on c textured films indicate a non linear relation between Tc and the microscopic parameter which determines its pressure dependence.
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Castello, D., M. Jaime, and M. Núñez Regueiro. "Thermal conductivity of high temperature superconductor TlBaCaCuO." Solid State Communications 79, no. 11 (1991): 967–970.
Abstract: We have measured the thermal conductivity of ceramic samples of TlBaCaCuO between 2 and 250 K. At high temperatures it follows a constant behaviour down to the superconducting transition temperature where a sudden increase of the thermal conductivity occurs, attributed to reduced phonon scattering by condensating electrons. At low temperatures a T2 law is observed, confirming the assumption that it is a common feature in most of the high temperature superconducting oxides. Phonon scattering against tunneling systems analogous to those found in amorphous solids can explain this behaviour.
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Dhalle, M., W. Boon, E. Osquiguil, C. Van Haesendonck, Y. Bruynseraede, J. Kwarciak, and O. Van Der Biest. "Correlation between critical current and resistivity in YBa2Cu3O7." Physica C: Superconductivity and its applications 185-189, no. PART 4 (1991): 2447–2448.
Abstract: Critical current versus temperature measurements were carried out in ceramic YBa2Cu3O7 samples. The samples were all prepared using the same sintering procedure, but starting from powders obtained by different wet and dry methods. All samples showed a linear Jc vs. T behaviour, typical of Josephson weak-link coupling, with a slope that depends on the preparation method. Using the Ambegaokar-Baratoff relation for Jc, the difference in slopes can be attributed to a change in the characteristic value of the junction resistance. This value turns out to be clearly correlated with the resistivity in the normal state.
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Duran, C., J. Yazyi, F. de la Cruz, D. J. Bishop, D. B. Mitzi, and A. Kapitulnik. "Flux-lattice melting, anisotropy, and the role of interlayer coupling in Bi-Sr-Ca-Cu-O single crystals." Physical Review B 44, no. 14 (1991): 7737–7740.
Abstract: We have used the high-Q mechanical-oscillator technique to probe the vortex-lattice structure in high-quality Bi-Sr-Ca-Cu-O single crystals over a wide range of magnetic fields (200 Oe to 40 kOe), and relative orientations θ between the magnetic field and the crystalline c^ axis. In addition to the large softening and dissipation peak previously observed and interpreted as due to flux-lattice melting, another distinctly different peak at higher temperatures is seen. The temperatures where the dissipation peaks take place are solely defined by the parallel component of the field cosθ, while the restoring force on the oscillator is due to both field components. We suggest that the two peaks are due to the softening of interplanar coupling at the low-temperature peak, and melting or depinning of the two-dimensional pancake vortices at the higher-temperature peak.
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Fernandes, A. A. R., J. Santamaria, S. L. Bud’ko, O. Nakamura, J. Guimpel, and I. K. Schuller. "Effect of physical and chemical pressure on the superconductivity of high-temperature oxide superconductors." Physical Review B 44, no. 14 (1991): 7601.
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Fraga, G. L. F., D. E. Brandao, and J. G. Sereni. "Specific heat of X2MnSn (X = Co, Ni, Pd, Cu), X2MnIn (X = Ni, Pd) and Ni2MnSb Heusler compounds." Journal of Magnetism and Magnetic Materials 102, no. 1-2 (1991): 199–207.
Abstract: Results of low-temperature specific heat measurements (1.5-8.0 K) on X2MnSn (X = Co, Ni, Pd, Cu), X2Mnln (X = Ni, Pd) and Ni2MnSb Heusler compounds are presented. All the compounds, except the cobalt based one, exibit a lattice spectrum anomaly described by an Einstein's term (soft-phonons). For all but one compound, the experimental values of the electronic specific heat coefficients are, at least, twice as big as the theoretical estimates. For two compounds it was possible to determine the magnetic effective field on Mn nuclei.
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Ghamaty, S., B. W. Lee, J. J. Neumeier, G. Nieva, and M. B. Maple. "Low-temperature specific heat of the Y1-xPrxBa2Cu3O7-δ system." Physical Review B 43 (1991): 5430.
Abstract: Low-temperature specific-heat C measurements as a function of temperature T between 0.5 and 30 K are reported for Y1-xPrxBa2Cu3O7-δ compounds with x=0, 0.2, 0.3, 0.4, 0.6, 0.8, and 1.0. The Pr contribution to the specific heat of all of the samples can be described as the sum of a Pr nuclear Schottky anomaly of the form CN(T)=AT-2, a linear term CL(T)=γT, and a Pr magnetic anomaly. For compounds with x≤0.6, which are metallic and superconducting, the Pr magnetic specific-heat anomaly has the same temperature dependence as a Kondo anomaly. For the compounds with x≥0.8, which are insulating, the magnetic specific-heat anomaly is consistent with antiferromagnetic ordering of the Pr ions with Néel temperatures TN of 10.9 and 15.7 K for x=0.8 and 1.0, respectively. For T<TN, the antiferromagnetic specific-heat anomaly has the form CM(T)=MT3, characteristic of three-dimensional antiferromagnetic magnons.
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Guimpel, J., P. Høghøj, I. K. Schuller, J. Vanacken, and Y. Bruynseraede. "Scaling of the irreversibility line in a low temperature superconducting oxide." Physica C: Superconductivity 175, no. 1-2 (1991): 197–201.
Abstract: We have studied the critical field and irreversibility line on the magnetization of the ceramic oxide LiTi2O4. The irreversibility line scales with the critical field while the coherence length of the material changes by a factor of two. This universal behavior indicates that the origin of the irreversibility line does not depend on extrinsic factors and relies solely on the intrinsic superconducting parameters of the material.
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Kappler, J. P., E. Beaurepaire, G. Krill, J. G. Sereni, C. Godart, and G. L. Olcese. "Anomalous behaviour of X-ray absorption observed on the highly correlated cerium nitride (CeN) compound." Journal de Physique I 1 (1991): 1381–1387.
Abstract: In this study, we present recent X-ray Absorption Spectroscopy (XAS) results obtained on highly pure cerium nitride (CeN) compounds. CeN is the “archetype” of the strongly mixed-valent (MV) cerium compounds, where the ground state properties are governed by strong hybridization effects between the 4f and the conduction electrons. We will show that, in clear contradistinction with earlier results, the L ${\rm III,II}$ absorption edges of cerium in CEN do not exhibit the two contributions usually observed in strong MV systems. Indeed, in all cases only one single white line is observed. This anomalous behaviour is related with similar results obtained recently on in-situ prepared CeN studied by both L ${\rm III}$ absorption and Ce 2p X-ray photoemission (XPS). The possible influence of the presence of p conduction states to explain this anomalous behaviour is addressed.
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Kappler, J. P., M. J. Besnus, A. Herr, A. Meyer, and J. G. Sereni. "Crossover between intermediate valence and magnetic order in CeRh1-xPdx." Physica B: Condensed Matter 171, no. 1-4 (1991): 346–349.
Abstract: Magnetic, resistivity and specific-heat measurements on the system CeRh1-xPd(x) are presented. The results indicate a continuous decrease of the hybridization when substituting Pd for Rh in the intermediate-valence compound CeRh. The transition to a magnetically ordered state occurs near x = 0.4. The experimental data suggest the coexistence of Kondo effect and magnetic order for Pd contents around 40-50 at.%. The present results show evidence for a crossover from an IV state with full degeneracy through Kondo-lattice behaviour to a local-moment magnetic state.
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